Coordinated MultiPoint (COMP) transmission/reception is an advanced technology for cellular communication networks to improve coverage, support high data rates, improve cell-edge throughput and/or to increase system throughput.
Downlink COMP generally implies dynamic coordination among multiple geographically separated transmission points, and uplink COMP generally implies coordination among multiple geographically separated reception points. In general, the basic idea is to perform joint transmission in the downlink by coordinating transmission from multiple points to one or more user terminals, and likewise to perform joint detection in the uplink by jointly processing radio signals received at multiple points.
As an intermediate step towards general COMP operation, so-called intra-site cooperation where different sectors of the same radio base station are coordinated has been proposed in reference [1].
It is also possible to coordinate different sectors belonging to different sites, so-called inter-site cooperation, where the data has to be exchanged between the involved radio base stations.
However, inter-site cooperation between different radio base stations provides many challenges on the way to a viable and practical solution, as outlined in reference [1]. Intra-site cooperation within the same radio base station is much easier to implement, since this approach only requires node internal transfer of data, and the delay due to the cooperation is almost negligible for intra-site cooperation. In addition, intra-site cooperation may already be realized with existing state-of-the art system, at least for the uplink, since no external signaling is involved and no hence further standardization would be required for that purpose.
Reference [2] describes a concept of distributed cooperation where base stations (BS) communicate directly via a BS-BS interface without central control. A serving base station can request cooperation from one or more supporting base stations, and by collecting In-phase and Quadrature-phase (IQ) samples from the antenna elements of the supporting base station or base stations, the serving base station can virtually increase its number of receive antennas. If the base stations of one eNodeB cooperate the required BS-BS interface can be eNodeB internal. If on the other hand, base stations of different eNodeBs cooperate, the IQ samples are exchanged via the dedicated X2 interface, the specification of which would have to be enhanced.
In general, high speed interfaces for inter-site cooperation are costly to deploy.
Although significant advances have been made in this area of research, there is still a general need for improved COMP operation in cellular radio communication networks and in particular with respect to the exchange of IQ samples between radio base stations.